Working with the anthropologist Russell Hill, [ evolutionary psychologist Robin] Dunbar pieced together the average English household’s network of yuletide cheer. The researchers were able to report, for example, that about a quarter of cards went to relatives, nearly two-thirds to friends, and 8 percent to colleagues. The primary finding of the study, however, was a single number: the total population of the households each set of cards went out to. That number was 153.5, or roughly 150.

This was exactly the number that Dunbar expected. Over the past two decades, he and other like-minded researchers have discovered groupings of 150 nearly everywhere they looked. Anthropologists studying the world’s remaining hunter-gatherer societies have found that clans tend to have 150 members. Throughout Western military history, the size of the company—the smallest autonomous military unit—has hovered around 150. The self-governing communes of the Hutterites, an Anabaptist sect similar to the Amish and the Mennonites, always split when they grow larger than 150. So do the offices of W.L. Gore & Associates, the materials firm famous for innovative products such as Gore-Tex and for its radically nonhierarchical management structure. When a branch exceeds 150 employees, the company breaks it in two and builds a new office.

It is impossible for Americans to accept the extent to which the Colonial period—including our most sacred political events—was suffused with alcohol. Protestant churches had wine with communion, the standard beverage at meals was beer or cider, and alcohol was served even at political gatherings. Alcohol was consumed at meetings of the Virginian and other state legislatures and, most of all, at the Constitutional Convention.

Indeed, we still have available the list of beverages served at a 1787 farewell party in Philadelphia for George Washington just days before the framers signed off on the Constitution. According to the bill preserved from the evening, the 55 attendees drank 54 bottles of Madeira, 60 bottles of claret, eight of whiskey, 22 of porter, eight of hard cider, 12 of beer, and seven bowls of alcoholic punch.